1. Field of the Invention
The present invention relates to a communication adapter which connects a PDA personal digital assistant) to a communication network and a network system using the communication adapters.
2. Description of Related Art
In a communication network system such as a LAN (local area network), as FIG. 6 shows, a plurality of PDAs 30 are capable of communicating with each other via a cable 31 and radio waves 32. As FIG. 7 shows, in order to connect a PDA 30 such as a note-type personal computer to such a communication network system 30, a communication adapter such as a PC card 35 or any other suitable adapter may be used.
There are two types of PC cards 35. One is for cable communication, and the other is for radio communication. When the PDA 30 accesses the communication network 33 via the cable 31, a PC card 35a for cable communication is inserted in the PDA 30. On the other hand, when the PDA 30 accesses the communication network 33 via the radio waves 32, a PC card 35b for radio communication is inserted in the PDA 30.
Thus, every PC card 35 enables a PDA 30 to access a communication network 33 via either a cable or via radio waves, and a PC card 35 which is suited for the access method between the PDA 30 and the communication network 33 must be inserted in the PDA 30.
Therefore, when the PDA 30 is expected to be able to access the communication network 33 via a cable and via radio waves, both the PC card 35a for cable communication and the PC card 35b for radio communication must be provided, which is costly.
Also, when the access method between the PDA 30 and the communication network 33 is switched from cable communication to radio communication or from radio communication to cable communication, the PC card 35a inserted in the PDA 30 must be replaced with the PC card 35b, or the PC card 35b inserted in the PDA 30 must be replaced with the PC card 35a. 
In addition, as shown in FIG. 6, in order to enable radio communication of the PDAs 30 through the communication network 33, an access point device 36 is required which makes conversions of signals between a cable communication form and a radio communication-form to relay these signals, which is also costly.